A rail adjustment system for a vehicle seat usually comprises a lower rail which is mounted such that it is fixed on the vehicle, and an upper rail which is connected to the vehicle seat and is mounted in a linearly adjustable manner in relation to the lower rail. The vehicle seat can be positioned in the longitudinal direction of the vehicle therewith. The rail adjustment system is assigned a locking device by means of which the upper rail is locked to the lower rail in a desired longitudinal position of the vehicle seat.
The locking device has to secure the vehicle seat in an adjusted longitudinal position, in particular under extreme applications of force that occur in a crash situation. At the same time, it is desirable for the locking device to be actuatable ergonomically and, in particular, simply and without a relatively great effort.
A locking device known from DE 203 13 951 U1 comprises a plurality of locking bolts which are arranged one behind another and can be lowered vertically, and a lever element which is mounted pivotably about a horizontal pivot axis parallel to the direction in which the locking bolts are arranged. For unlocking purposes, the lever element engages on the end side by means of fork-shaped extensions behind the locking bolts in the unlocking direction. The locking device is mounted on the upper rail of a rail adjustment system of the type mentioned at the beginning, with the lower rail having a perforated grid with spaced-apart latching openings for receiving the locking bolts. The locking bolts are provided with spring elements on their circumference. Said spring elements press the locking bolts in the locking direction, are compressed by the lever element during an unlocking operation and, as a result, form a resetting force.
The distance between the latching openings on the perforated grid of the lower rail differs from the distance between the locking bolts of the locking device, and therefore, in the locked state of the rail adjustment system, not all of the locking bolts are fully lowered, but rather at least one of the locking bolts is situated in a prestressed state between two latching openings on the lower rail. At high acceleration—for example caused by a crash situation—the vehicle seat is moved due to the inertia, and therefore the lowered locking bolts absorb part of the force of inertia of the vehicle seat and convert it into deformation forces. The upper rail is displaced in the process in relation to the lower rail. The prestressed locking bolt briefly slides over the next free latching opening in the direction of movement and is lowered by the spring force of the spring element, and therefore the locking bolt is activated as an additional means of securing from the rear.
The lever element of the known locking device has a surface which, with respect to the pivot axis, is arranged lying opposite the fork-shaped extensions and which is designed for the introduction of force by means of further means. To unlock the locking bolts, the surface is pressed in the locking direction. The size and shaping of the surface are determined so as to reduce, in accordance with lever principles, the force to be applied to the force introduction point of the surface for the unlocking of the locking bolts. The longer the lever arm on the side of the surface facing the pivot axis, the proportionally smaller the unlocking force to be applied turns out to be.
The surface of the lever element and the further means which are designed for introducing force to the surface are, overall, space-intensive. If the locking device is arranged on the lower side of the seat, the surfaces engage in the region between the seat rails, as a result of which the construction space and the freedom of design for the configuration of the geometry on the lower side of the seat may be limited.